TypedArray.prototype.findLast()

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since August 2022.

The findLast() method of TypedArray instances iterates the typed array in reverse order and returns the value of the first element that satisfies the provided testing function. If no elements satisfy the testing function, undefined is returned. This method has the same algorithm as Array.prototype.findLast().

Try it

function isNegative(element /*, index, array */) {
  return element < 0;
}

const int8 = new Int8Array([10, 0, -10, 20, -30, 40, 50]);

console.log(int8.find(isNegative));
// Expected output: -30

Syntax

findLast(callbackFn)
findLast(callbackFn, thisArg)

Parameters

callbackFn

A function to execute for each element in the typed array. It should return a truthy value to indicate a matching element has been found, and a falsy value otherwise. The function is called with the following arguments:

element: The current element being processed in the typed array.
index: The index of the current element being processed in the typed array.
array: The typed array findLast() was called upon.

thisArg Optional

A value to use as this when executing callbackFn. See iterative methods.

Return value

The last (highest-index) element in the typed array that satisfies the provided testing function; undefined if no matching element is found.

Description

See Array.prototype.findLast() for more details. This method is not generic and can only be called on typed array instances.

Examples

Find the last prime number in a typed array

The following example returns the last element in the typed array that is a prime number, or undefined if there is no prime number.

function isPrime(n) {
  if (n < 2) {
    return false;
  }
  if (n % 2 === 0) {
    return n === 2;
  }
  for (let factor = 3; factor * factor <= n; factor += 2) {
    if (n % factor === 0) {
      return false;
    }
  }
  return true;
}

let uint8 = new Uint8Array([4, 6, 8, 12]);
console.log(uint8.findLast(isPrime)); // undefined (no primes in array)
uint8 = new Uint8Array([4, 5, 7, 8, 9, 11, 12]);
console.log(uint8.findLast(isPrime)); // 11

Note: The isPrime() implementation is for demonstration only. For a real-world application, you would want to use a heavily memoized algorithm such as the Sieve of Eratosthenes to avoid repeated calculations.

Specifications

Specification
ECMAScript® 2026 Language Specification # sec-%typedarray%.prototype.findlast